Coupling pieces of the type in question here, called "Twistlock" in the specialized jargon, are used predominantly during the transport of containers on ships. The coupling pieces are intended for reliably preventing shifts of the containers relative to the ship on the one hand and relative to one another on the other hand.
The invention starts from a coupling piece, such as is described, for example, in German Offenlegungsschrift 2,204,915, in particular a so-called three-function twistlock, In this coupling piece, the mutually opposite crossbars are arranged on the locking bolt with an angular offset relative to one another and can be brought into three different coupling positions. In a released position, with the lower crossbar prelocked, the upper crossbar is in an open position for insertion into the lower corner fitting of an upper container. After insertion into the corner fitting of the upper container, the coupling piece is prelockable, with the upper crossbar prelocked and the lower crossbar open. In this position, the upper container can be introduced, together with the coupling piece, into a corresponding upper corner fitting of a lower container. The crossbars can then be brought into their locking position, in which the two containers are connected by means of the coupling piece.
A disadvantage of this known coupling piece is that manual intervention is necessary several times in order to fit it and remove it, first with respect to the prelocking of the coupling piece and second with respect to the final locking after the containers have been placed on one another. The last locking step in particular presents special difficulties in practice, because it has to be carried out after the containers have been stacked on one another and, according to experience, access to the coupling pieces has become more difficult. Furthermore, the final locking of the coupling pieces involves danger to the person entrusted with this, because, to do this, he has to climb onto or between several container stacks.